GUI editor for XML files

I'm wondering if there are open source GUI tools for editing XML files. What I need is a tool, preferably Java tool, which reads an XML file and shows a GUI representing the XML fields and lets the user to modify the data and save it back. A very good example of application of this tool is editing XML configuration files.

Joe, there's lots of XML editors out there. Google for "xml editor" and you will find them. Why do you need an open-source XML editor, though? Are you planning on getting involved and improving it? If you're just looking for a free one, there's plenty.